Gear making

ABSTRACT

Apparatus for making gears, featuring a workpiece support mounted to provide rotation of the workpiece about its axis at a basic rate; a cutter having profile generating cutting edges mounted for rotation about a cutter axis at a basic rate bearing a ratio to the basic workpiece rate dependent upon the ratio of the number of profiles being generated to the number of profile generating cutting edges in the cutter, the cutter axis being at an angle to the workpiece axis which differs from 90* by an angle other than the helix angle (taken at the generating circle) of the gear being made, the cutter and workpiece being mounted for relative translation axially of the workpiece; and an element responsive to that relative translation to add to or subtract from the basic workpiece rate a rate of rotation to which the rate of translation bears a ratio equal to the desired lead of the gear being made; whereby successive cuts made in each toothspace are tangent to the adjacent profile at lines oblique to the workpiece axis and extending generally between the fillet and tip of the profile, and between successive cuts tangent to any one desired profile there will intervene a complete revolution of the workpiece.

United States Patent Maker May 16, 1972 54] GEAR MAKING 57 ABSTRACT [72]Inventor: Paul Maker, Marion, Mass. Apparatus for making gears,featuring a workpiece support Assignee: Bird Island, Inc. Boston Massmounted to provide rotation of the workpiece about ts axis at a basicrate; a cutter havmg profile generating cutting edges [22] Filed: Feb.16, 1970 mounted for rotation about a cutter axis at a basic ratebearing a ratio to the basic workpiece rate dependent upon the ratio of[21] Appl' ll503 the number of profiles being generated to the number ofprofile generating cutting edges in the cutter, the cutter axis [52][1.5. CI. 90/3, 29/ 105 R being at an angle to the workpiece axis whichdiffers from 90 [51] Int. Cl. ..B23f 5/20 b an angle ther than the helixangle (taken at the generating of Search 4, 6, 1, 9 circle) ofthe gearbeing made the cutter and workpiece being mounted for relativetranslation axially of the workpiece; and

[56] References C'ted an element responsive to that relative translationto add to or subtract from the basic workpiece rate a rate of rotationto UNITED STATES PATENTS which the rate of translation bears a ratioequal to the desired 1,516,524 1 1/1924 Fellows ..90/3 lead of the gearbeing made; whereby successive cuts made in 1,877,104 9/1932 Wildhaber..29/ 103 each toothspace are tangent to the adjacent profile at lines1,983,019 1934 D L m oblique to the workpiece axis and extendinggenerally 2,315,068 3/1943 Matthews ..90/4 bet n the fillet and tip ofthe profile, and between succes- Primary Examiner-Gil WeidenfeldAttorney-Robert E. Hillman sive cuts tangent to any one desired profilethere will intervene a complete revolution of the workpiece.

15 Claims, 15 Drawing Figures P'ATENTEnnAmm 3.662.650

sum 3 or 4 I52 FIG 7 FIG 3 II 1202 um FIG 6 202 FIG 5 L GEAR MAKING Thisinvention relates to making gears with apparatus of the general typedisclosed in pending U.S. Pat. application Ser. No. 844,925, filed byPaul Maker on July 25, 1969, now U.S. Pat. No. 3,595,130.

Objects of the invention are to provide for high speed, high qualitygear making, using a rotary cutter, and continuously indexing theworkpiece; yet making possible the production of gears of any desiredhelix angle, with straight roots, and with highly accurate toothprofiles of any of a wide variety of shapes finished to a uniform depthover the entirety of an arbitrarily large face width. Other objects areto provide in a simple and reliable manner for accurate location ofcutting tools in the cutter, so that variation in too] dimensions (e.g.,due to sharpening) will not affect cutting edge position.

The invention features a workpiece support mounted to provide rotationof the workpiece about its axis at a basic rate; a cutter having profilegenerating cutting edges mounted for rotation about a cutter axis at abasic rate bearing a ratio to the basic workpiece rate dependent uponthe ratio of the number of profiles being generated to the number ofprofile generating cutting edges in the cutter, the cutter axis being atan angle to the workpiece axis which differs from 90 by an angle otherthan the helix angle (taken at the generating circle) of the gear beingmade, the cutter and workpiece being mounted for relative translationaxially of the workpiece; and an element responsive to that relativetranslation to add to or subtract from one of the basic rates adifferential rate of rotation to which the rate of translation bears aratio dependent upon the desired lead of the gear being made; wherebysuccessive cuts made in each toothspace are tangent to the adjacentprofile at lines oblique to the workpiece axis and extending generallybetween the fillet and tip of the profile, and between successive cutstangent to any one desired profile there will intervene a completerevolution of the workpiece. In preferred embodiments the differentialrate is added to or subtracted from the basic rate of the workpiece, andits ratio with the rate of translation is equal to the desired lead; thesuccessive cuts are tangent to the profile at lines oblique to theworkpiece axis; the profile generating cutting edges lie in a singlesurface of revolution, and are linear when involute profiles are desiredand non-linear otherwise, the relative translation extendingsufficiently to cause the entire workpiece to effectively move axiallypast the plane of deepest penetration of the cutter into the workpiece;the cutter has a tool-holding body with removable tools arranged so thatthe cutting edges are spaced uniformly around the periphery of the body;a second cutter is constructed and disposed in a manner analagous to thefirst cutter for generating profiles on the opposite sides of the teethfrom the profiles generated by the first cutter, the two cutter axesbeing coplanar but non-parallel to each other, the cutters being mountedfor translation along their respective axes toward the workpiece axis;the cutter and workpiece are mounted additionally for relativetranslation along a path nonparallel to the workpiece axis, the basicrate of rotation of the cutter or of the workpiece being changed, uponoccurrence of the last mentioned relative translation, by a differentialrate dependent upon the rate of the translation, so that for eachdesired tooth profile the profile generating edges will make a series ofcuts respectively adjacent to but not intersecting the desired profile,the passes of the profile generating edges being tangent to an imaginarycontinuation above the workpiece of the desired profile, a completerevolution of the workpiece intervening between successive ones of thelast mentioned cuts adjacent to any one desired profile; and theapparatus has an infeed mode during which only the relative translationnon-parallel to the workpiece axis occurs, and an axial feed mode duringwhich only the translation axially of the workpiece occurs, profilegeneration occuring during the axial feed mode at the intersection of asurface of action tangent to the generating circle with the path of theprofile generating edges, the cutter axes being located relative to theworkpiece during the infeed mode so that the surface of action is notintersected within the workpiece by the cutters.

Other objects, features, and advantages will appear from the followingdescription of a preferred embodiment of the invention, taken togetherwith the attached semi-schematic drawings thereof, in which:

FIG. 1 is an isometric view of a gear making machine;

FIG. 2 is a fragmentary plan view, partially broken away and sectioned,of the machine of FIG. 1;

FIG. 3 is a fragmentary elevational view of the workpiece supportportion of the machine;

FIG. 4 is an axial section of a portion of a cutter;

FIG. 5 is a fragmentary elevational view taken along 55 of FIG. 4;

FIG. 5a is a view similar to FIG. 5 of a smaller portion of the othercutter;

FIG. 6 is a sectional view taken along 66 of FIG. 5;

FIG. 7 is an end view of one tool;

FIG. 8 is a view along 88 of FIG. 7;

FIG. 9 is a view along 9-9 of FIG. 7;

FIG. 10 is an isometric view of a tool;

FIG. 11 is an isometric view of a gear to be made;

FIG. 12 is a diagramatic axial section of a workpiece, shown inconventional fashion as a spur gear, showing selected lines along whichsuccessive tools make cuts tangent to the desired profile during theaxial feed mode;

FIG. 13 is a plan view of a non-involute profile; and

FIG. 14 is a plan view of a profile generating cutting edge useful forgenerating the profile of FIG. 13.

Two cutter assemblies 10 and 12 (FIGS. 1, 2) are mounted on machineframe 14 for sliding linear movement in grooves 16 and 18, respectively,under the power of motors 20 and 22. The cutter assemblies includecutters 30 and 32 mounted to rotate about coplanar axes 34 and 36respectively parallel to the directions of grooves 16 and 18 making anobtuse angle with each other.

Work support assembly 40 also mounted on frame 14 includes a pair ofwork support spindles 42 and 44 rotatable about a common axis 46.Spindles 42 and 44 carry between themselves a workpiece 45 and arepositioned on a head 48 mounted for angular adjustment in housing 50, sothat the angle between axis 46 and axes 34 and 36 can be changed. Head48 is bolted to cylindrical sleeve 54 in housing 50. Worm 56 meshes withgrooves 58, so that rotation of the worm (under control of handle 60,FIG. 1) causes corresponding rotation of the sleeve. Screw 64 isjournalled in housing 50 and engages threads in a bore in block 66 keyedin circumferential groove 68 of sleeve 54, so that rotation of screw 64causes movement of sleeve 54 along its own axis.

Mounted to rotate between head 48 and sleeve 54 is ring 70 (FIGS. 2-3)one portion of which is a spur gear 72 in mesh with drive gear 73 onshaft 74, another portion of which is a bevel gear 76 in mesh with abevel gear 78 surrounding spindle 44. Gear 78 has an inner projection 80which fits in helical groove 82 in spindle 44. Spindle 44 has acounterbore 90, and, with cylindrical post 92 of head 48, provides ahydraulic cylinder controlled by fluid fed through passage 94 in thehead.

Spindle 42 is mounted for rotary and axial movement in head 48, and isbiased toward spindle 44 by spring 96.

Cutter 30 (FIGS. 2-4) is carried on spindle 102 for rotation in housing104. Motor 20 drives shaft 106 threaded in housing 104 to move thehousing in groove 16. Shaft 106 is coupled to one input of difi'erential110 through gears 112 and 114. Shaft 116, driven by shaft 74 throughbevel gears 118 and 120, is coupled to the other input of difierential110 through gears 122 and 124. The differential sums the rotations ofshafts 106 and 116, and drives, through its output, shaft which isarranged to rotate spindle 102 through gears 130a and 1301:, whileallowing axial movement of the spindle when shaft 106 rotates.

Cutter assembly 12 is similarly constructed and driven, with shaft 132driven through bevel gears 118 and 134 providing one input to thecorresponding differential (not shown). The differential is arranged tosubtract from the rate of rotation of shaft 132 the rate of rotation ofthe shaft (not shown) corresponding to shaft 106.

Shaft 74 is driven by motor 140.

Cutter 30 has a head 150 (FIGS. 4-6) bolted on spindle extension 151with a carbide tool 152 clamped in each of a series of radial recesses154 equally spaced around the head. The tools are held in place byclamping ring 156 bolted to head 150.

Each tool 152 (FIGS. 7-10) has a pair of flat surfaces 160 and 162meeting at an acute angle to define straight-line profile generatingcutting edge 164, and a cylindrically rounded surface 166. At thecutting end 168 of the tool surface 160 acts as a leading face 170bounded by edge 164, concave roughing edge 172, and cutting tip 174having a radius of curvature matching that of the fillet of the gear tobe made. Face 170 is tilted at a small clearance angle relative to animaginary reference plane 180 (FIG. 10), and the side and tip surfaces162, 182, and 184 all slope away from face 170 at small clearance anglesto planes normal to reference plane 180, as indicated in FIG. 10.

Each groove 154 in head 150 has a V-shaped portion with surfaces 190 and192 at an angle to each other equal to the angle between tool surfaces160 and 162, so that the tool will fit tightly into the groove with thesurfaces defining edge 164 directly positioned by contact with the head.The tools are radially located by abutment against positioning ring 193(FIG. 4). Clamping ring 156 has a tooth 194 (FIG. 5) which extends intorectangular portion 196 of each groove 154, with oblique surface 198against surface 166 of the tool. Ring 156 has a circumferential slot 200below teeth 194, across which pass tightening bolts 202 (one for eachpair of tools). The tools are firmly clamped in place by turning bolts202 to force tool surfaces 160 and 162 against head surfaces 190 and192, respectively. Thus, edges 164 are always located in the sameposition, even after repeated sharpenings by grinding of surfaces 160and 162.

Groove surfaces 190 and 192 are located so that all tool edges 164 liein a single plane perpendicular to the cutter axis, and all referenceplanes 180 are at an angle to cutter axis 34 dependent upon the desiredhelix angle of the gear being made (taken at the generating circle ofthe gear) and the angle between axes 34 and 46.

Cutter 32 (FIG. 5a) is similarly constructed, with its tools beingmirror images of tools 152. The corresponding reference planes of thetools of cutter 32 are tilted with respect to axis 36 in the oppositedirection (from the point of view of an observer watching a tool fromeach cutter simultaneously passing through the workpiece) from thedirection in which the reference planes of tools 152 are tilted withrespect to axis 34. The leading faces of all tools face workpiece 45 asthey approach the workpiece from above when the cutters are rotating inthe directions indicated in FIG. 1.

The ratio' of the common rate of rotation of cutters 30 and 32 (takenwhen the cutter assemblies are stationary in their slots and theworkpiece is not moving along axis 46) to the rate of rotation ofspindle 44 is equal to the ratio of the desired number of teeth in thegear being made to the number of tools per cutter.

The lead of helical groove 82 in spindle 44 is equal to the lead of thegear being made.

Differential l 10, and the corresponding differential for cutter 32, arechosen so that the differential rate of rotation added to a cutter upontranslation of the cutter assembly along its slot is related to the rateof that translation in a manner appropriate to the desired gear toothprofile being generated (e.g., the differential rate of cutter rotationbeing linearly related to the rate of cutter translation when involuteprofiles are being generated).

Operation of the above described apparatus, to make from a workpiece 45a gear 220 (FIG. 11) having teeth 222 with involute tooth profiles 223and 2230 on their respectively opposite sides, and fillets 224, consistsof an infeed of the cutters to the desired root depth, followed by anaxial feed of the workpiece.

Involute generation involves, of course, an effective relative rollingmotion between cutter and workpiece, and, in

machines of this general type, all generation occurs at the intersectionof the plane of action (tangent to the base circle) with the paththrough which the cutting edges move. Prior to the infeed the rotatingcutters are spaced from the workpiece, with spindles 42 and 44 lowered(from the point of view of FIG. 1) so that the plane of action will notintersect the cutters within the workpiece during the infeed. Handle 60is adjusted so that axis 46 is tilted with respect to each cutter axisby an angle which differs from by an angle other than the helix angle ofthe gear being made (taken at the generating circle), making use of theformulas set forth above. With motor operating, motors 20 and 22 areactuated to advance cutter assemblies 10 and 12 along slots 16 and 18toward the workpiece. The tools will begin to remove stock from the topof the workpiece adjacent to, but not intersecting, the desired toothprofiles. Considering the action of cutter 30 as typical, one tool 152will make a small notch at the top of the workpiece adjacent one toolposition, the next tool will cut a corresponding notch adjacent the verynext tooth position, and so on, so that a corresponding notch will becut 'on the corresponding side of each tooth before a second cut is madeon the same side of the first tooth. As screw 106 turns, translating thecutter, a differential rotation proportional to that translation isadded to the basic rotation of the cutter, through differential 110. Thelinear advance and differential rotation of the cutter constitute aneffective relative rolling motion between the workpiece and the cutterand cause the successively deeper passes by tool edges 164 adjacent anygiven tooth to be tangent to the imaginary continuation above theworkpiece of the desired involute profile 223, the lines of tangencybeing oblique to the workpiece axis and successively approaching thedesired root circle of gear 220. This imaginary tangency above theworkpiece ensures that the cuts will not intersect the desired profileswithin the workpiece. The infeed is continued to the desired depth.

At the end of the infeed motors 20 and 22 are stopped, and fluid isforced through passage 94 to gradually raise spindles 44 and 42 and theworkpiece. The tools of each cutter will continue to, in effect, meshwith the emerging teeth of the workpiece, and to make successive obliquecuts in each toothspace identical to each other except for their axialposition on the workpiece. As the plane of action within the gearintersects the profile generating edges, involute profiles will begenerated by cuts along oblique lines extending, after the early cutswhich do not reach the fillet, from fillet to tip of each tooth.Projection 80 and groove 82 give the workpiece an extra rotation relatedto the axial feed of the workpiece to produce the desired lead in gear220. The involute profile is generated during the axial feed by virtueof the fact that each cut removes stock at every radial (of theworkpiece) position along the desired profile, along a path that istangent to the profile because of the linear nature of the profilegenerating tool edges and the constant ratio of the respective rates ofcutter and workpiece rotation. The axial feed continues until thedesired profiles have been generated across the entire face width of thegear, the total length of axial feed being greater than the face width,as is required to finish all comers of the profiles. Selected lines 232tangent to the profile, taken from the sequence of successive cutsduring the axial feed, are shown in FIG. 12, for a typical profile 223.

Tool tips 174 will cut the tooth fillets, which will be straight despitethe fact that the tools move through an arc, since the entire workpiecewill have been fed axially past the plane of deepest tool penetration,that plane being defined by and including the cutter axis and the commonnormal to the cutter and workpiece axes. Tool edges 172 rough outmaterial in the paths of the tools of cutter 32.

Cutter 32 operates in generally the same way as cutter 30, to generateprofiles 223a. During the infeed the difierential cutter rotationproportional to the cutter feed is subtracted from the basic rate ofcutter rotation. Since the top of the workpiece is tilted away fromcutter 32, the cut lines 232a which generate the involute slopedownwardly toward fillets 224.

The infeed portion of the generating cycle described above can beomitted by advancing the cutters to the position where the tools sweepto the desired depth while the workpiece is lowered sufiiciently to becompletely out of the paths of the tools. Exclusive use of axial feedcan be particularly advantageous in generation of non-involute profiles,and especially concave (i.e., undercut) profiles, since, for axial feed,the generating motion from root to tip of the profile occurs, and inessentially identical fashion, during each cut, and can be controlledcompletely by the geometry of the profile generating tool edges 164.Thus, the tool edge needed to generate the desired non-involute profilecan be derived from the profile geometry by conventional graphicalconvergent techniques, using successive cutting trials, andcorresponding tool re-design, to gradually arrive at the optimumgenerating edge. FIG. 14 shows a tool with a cutting edge 164' usefulfor generating the profiles 240 shown in FIG. 13.

If the apparatus is operated in its infeed mode with the cutter axesperpendicular to the workpiece axis, and with the workpiece raised sothat the profile generating cutting edges intersect the plane of actionacross the entire workpiece facewidth, involute profiles will becompletely generated during the infeed in the manner described in detailin the above identified pending application.

Other embodiments will appear to those skilled in the art and are withinthe following claims.

What is claimed is:

1. Apparatus for generating tooth profiles in a gear, comprising aworkpiece support,

means mounting said support for rotation of a workpiece about an axis ata basic rate; a cutter having profile generating cutting edges lyingalong straight lines and, I

means mounting said cutter for rotation about a cutter axis at a basicrate bearing a ratio to the basic workpiece rate dependent upon theratio of the number of said profiles being generated to the number ofsaid profile generating cutting edges in said cutter,

said cutter axis being out of perpendicularity with the workpiece axisby an angle other than the helix angle of said gear taken at thegenerating circle,

means mounting said cutter and said support for relative translationaxially of said workpiece; and

means responsive to said relative translation to add to or subtract fromone of said basic rates a differential rate of rotation to which therate of said translation bears a ratio dependent upon the desired leadof said gear;

whereby successive cuts made in each toothspace are tangent to theadjacent desired profile at lines oblique to said workpiece axis andextending generally between the fillet and tip of said profile, andbetween successive cuts tangent to any one desired profile there willintervene a complete revolution of said workpiece.

2. Apparatus for generating tooth profiles in a gear, comprising aworkpiece support means mounting said support for rotation of aworkpiece about an axis at a basic rate;

a pair of cutters each having profile generating cutting edges meansmounting said cutters for rotation about a respective cutter axis at abasic rate bearing a ratio to the basic workpiece rate dependent uponthe ratio of the number of said profiles being generated to the numberof said profile generating cutting edges in a said cutter,

means mounting said cutters and said support for relative translationaxially of said workpiece; and

means responsive to said relative translation to add to or subtract fromone of said basic rates a difi'erentia] rate of rotation to which therate of said translation bears a ratio dependent upon the desired leadof said gear;

whereby successive cuts made in each toothspace are tangent to theadjacent desired profile at lines extending generally between the filletand tip of said profile, and between successive cuts tangent to any onedesired profile there will intervene a complete revolution of saidworkpiece,

said cutters being arranged to generate respective profiles on theopposite sides of teeth of said gear.

3. The apparatus of claim 1 wherein said profile generating cuttingedges lie on a single surface of revolution.

4. The apparatus of claim 2 wherein said profile generating cuttingedges are non-linear, and said profiles are non-involute.

5. The apparatus of claim 1 wherein said cutter has a toolholding bodywith removable tools arranged so that said profile generating cuttingedges are spaced uniformly around the periphery of said body.

6. The apparatus of claim 1 further comprising a second cutterconstructed and disposed in a manner analagous to said first mentionedcutter for generating profiles on the opposite sides of teeth from saidprofiles generated by said first mentioned cutter.

7. The apparatus of claim 6 wherein the two cutter axes are non-parallelto each other and means mounting said cutters provide for translationalong their respective axes toward said workpiece axis, in addition tosaid relative translation.

8. The apparatus of claim 7 wherein said cutter axes are coplanar.

9. The apparatus of claim 1 wherein said means mounting said cutter andsaid support additionally provide for relative translation along a pathnon-parallel to said workpiece axis, one of said basic rates of rotationbeing changed, upon occurrence of said last mentioned relativetranslation, by a differential rate dependent upon the rate of said lastmentioned translation, so that for each desired tooth profile saidprofile generating cutting edges will make a series of passesrespectively tangent to an imaginary continuation above said workpieceof said desired profile along a series of lines, said support and saidcutter being relatively positioned so that, during said last mentionedtranslation, said cutter does not intersect the surface of action onwhich are located said lines oblique to said workpiece axis, a completerevolution of said workpiece intervening between successive ones of saidsweeps tangent to any one said imaginary continuation of a desiredprofile.

10. The apparatus of claim 9 wherein only said relative translationnon-parallel to said workpiece axis occurs during an infeed mode, andonly said relative translation axially of said workpiece occurs duringan axial feed mode subsequent to said infeed mode.

11. The apparatus of claim 1 wherein said cutter rotates to a plane ofdeepest penetration into said workpiece, said plane being defined by andincluding said cutter axis and the common normal to said cutter andworkpiece axes, said relative translation extending sufficiently tocause the entire said workpiece to efiectively move axially past saidplane.

12. The apparatus of claim 2 wherein the two cutter axes are nonparallelto each other and means mounting said cutters provide for translationalong their respective axes toward said workpiece axis, in addition tosaid relative translation.

13. The apparatus of claim 2 wherein said cutter axes are coplanar.

14. Apparatus for generating tooth profiles in a gear, comprising aworkpiece support means mounting said support for rotation of aworkpiece about an axis at a basic rate;

a cutter having profile generating cutting edges, means mounting saidcutter for rotation about a cutter axis at a basic rate bearing a ratioto the basic workpiece rate dependent upon the ratio of the number ofsaid profiles being generated to the number of said profile generatingcutting edges in said cutter,

means mounting said cutter and said support for relative translationaxially of said work piece; and

means responsive to said relative translation to add to or subtract fromone of said basic rates a differential rate of rotation to which therate of said translation bears a ratio dependent upon the desired leadof said gear;

whereby successive cuts made in each toothspace are tangent to theadjacent desired profile at lines extending generally between the filletand tip of said profile, and between successive cuts tangent to any onedesired profile there will intervene a complete revolution of saidworkpiece,

said means mounting said cutter and said support providing additionallyfor relative translation along a path nonparallel to said workpieceaxis, said basic rate of rotation of said cutter or of said workpiecebeing changed, upon occurrence of said last mentioned relativetranslation, by a differential rate dependent upon the rate of said lastmentioned translation, so that for each desired tooth profile saidprofile generating cutting edges will make a series of passesrespectively tangent to an imaginary continuation above said workpieceof said desired profile along a series of lines, said support and saidcutter being relatively positioned so that, during said last mentionedtranslation, said cutter does not intersect the surface of action onwhich are located said lines at which said cuts are tangent to saiddesired profiles, a complete revolution of said workpiece interveningbetween successive ones of said sweeps tangent to any one said imaginarycontinuation of a desired profile.

15. The apparatus of claim 14 wherein only said relative translationnon-parallel to said workpiece axis occurs during an infeed mode, andonly said relative translation axially of said workpiece occurs duringan axial feed mode subsequent to said infeed mode.

* k I. l

1. Apparatus for generating tooth profiles in a gear, comprising aworkpiece support, means mounting said support for rotation of aworkpiece about an axis at a basic rate; a cutter having profilegenerating cutting edges lying along straight lines and, means mountingsaid cutter for rotation about a cutter axis at a basic rate bearing aratio to the basic workpiece rate dependent upon the ratio of the numberof said profiles being generated to the number of said profilegenerating cutting edges in said cutter, said cutter axis being out ofperpendicularity with the workpiece axis by an angle other than thehelix angle of said gear taken at the generating circle, means mountingsaid cutter and said support for relative translation axially of saidworkpiece; and means responsive to said relative translation to add toor subtract from one of said basic rates a differential rate of rotationto which the rate of said translation bears a ratio dependent upon thedesired lead of said gear; whereby successive cuts made in eachtoothspace are tangent to the adjacent desired profile at lines obliqueto said workpiece axis and extending generally between the fillet andtip of said profile, and between successive cuts tangent to any onedesired profile there will intervene a complete revolution of saidworkpiece.
 2. Apparatus for generating tooth profiles in a gear,comprising a workpiece support means mounting said support for rotationof a workpiece about an axis at a basic rate; a pair of cutters eachhaving profile generating cutting edges means mounting said cutters forrotation about a respective cutter axis at a basic rate bearing a ratioto the basic workpiece rate dependent upon the ratio of the number ofsaid profiles being generated to the number of said profile generatingcutting edges in a said cutter, means mounting said cutters and saidsupport for relative translation axially of said workpiece; and meansresponsive to said relative translation to add to or subtract from oneof said basic rates a differential rate of rotation to which the rate ofsaid translation bears a ratio dependent upon the desired lead of saidgear; whereby successive cuts made in each toothspace are tangent to theadjacent desired profile at lines extending generally between the filletand tip of said profile, and between successive cuts tangent to any onedesired profile there will intervene a complete revolution of saidworkpiece, said cutters being arranged to generate respective profileson the opposite sides of teeth of said gear.
 3. The apparatus of claim 1wherein said profile generating cutting edges lie on a single surface ofrevolution.
 4. The apparatus of claim 2 wherein said profile generatingcutting edges are non-linear, and said profiles are non-involute.
 5. Theapparatus of claim 1 wherein said cutter has a tool-holding body withremovable tools arranged so that said profile generating cutting edgesare spaced uniformly around the periphery of said body.
 6. The apparatusof claim 1 further comprising a second cutter constructed and disposedin a manner analagous to said first mentioned cutter for generatingprofiles on the opposite sides of teeth from said profiles generated bysaid first mentioned cutter.
 7. The apparatus of claim 6 wherein the twocutter axes are non-parallel to each other and means mounting saidcutters provide for translation along their respective axes toward saidworkpiece axis, in addition to said relative translation.
 8. Theapparatus oF claim 7 wherein said cutter axes are coplanar.
 9. Theapparatus of claim 1 wherein said means mounting said cutter and saidsupport additionally provide for relative translation along a pathnon-parallel to said workpiece axis, one of said basic rates of rotationbeing changed, upon occurrence of said last mentioned relativetranslation, by a differential rate dependent upon the rate of said lastmentioned translation, so that for each desired tooth profile saidprofile generating cutting edges will make a series of passesrespectively tangent to an imaginary continuation above said workpieceof said desired profile along a series of lines, said support and saidcutter being relatively positioned so that, during said last mentionedtranslation, said cutter does not intersect the surface of action onwhich are located said lines oblique to said workpiece axis, a completerevolution of said workpiece intervening between successive ones of saidsweeps tangent to any one said imaginary continuation of a desiredprofile.
 10. The apparatus of claim 9 wherein only said relativetranslation non-parallel to said workpiece axis occurs during an infeedmode, and only said relative translation axially of said workpieceoccurs during an axial feed mode subsequent to said infeed mode.
 11. Theapparatus of claim 1 wherein said cutter rotates to a plane of deepestpenetration into said workpiece, said plane being defined by andincluding said cutter axis and the common normal to said cutter andworkpiece axes, said relative translation extending sufficiently tocause the entire said workpiece to effectively move axially past saidplane.
 12. The apparatus of claim 2 wherein the two cutter axes arenon-parallel to each other and means mounting said cutters provide fortranslation along their respective axes toward said workpiece axis, inaddition to said relative translation.
 13. The apparatus of claim 2wherein said cutter axes are coplanar.
 14. Apparatus for generatingtooth profiles in a gear, comprising a workpiece support means mountingsaid support for rotation of a workpiece about an axis at a basic rate;a cutter having profile generating cutting edges, means mounting saidcutter for rotation about a cutter axis at a basic rate bearing a ratioto the basic workpiece rate dependent upon the ratio of the number ofsaid profiles being generated to the number of said profile generatingcutting edges in said cutter, means mounting said cutter and saidsupport for relative translation axially of said work piece; and meansresponsive to said relative translation to add to or subtract from oneof said basic rates a differential rate of rotation to which the rate ofsaid translation bears a ratio dependent upon the desired lead of saidgear; whereby successive cuts made in each toothspace are tangent to theadjacent desired profile at lines extending generally between the filletand tip of said profile, and between successive cuts tangent to any onedesired profile there will intervene a complete revolution of saidworkpiece, said means mounting said cutter and said support providingadditionally for relative translation along a path non-parallel to saidworkpiece axis, said basic rate of rotation of said cutter or of saidworkpiece being changed, upon occurrence of said last mentioned relativetranslation, by a differential rate dependent upon the rate of said lastmentioned translation, so that for each desired tooth profile saidprofile generating cutting edges will make a series of passesrespectively tangent to an imaginary continuation above said workpieceof said desired profile along a series of lines, said support and saidcutter being relatively positioned so that, during said last mentionedtranslation, said cutter does not intersect the surface of action onwhich are located said lines at which said cuts are tangent to saiddesired profiles, a complete revolution of said workpiece interveningbetween successive ones of sAid sweeps tangent to any one said imaginarycontinuation of a desired profile.
 15. The apparatus of claim 14 whereinonly said relative translation non-parallel to said workpiece axisoccurs during an infeed mode, and only said relative translation axiallyof said workpiece occurs during an axial feed mode subsequent to saidinfeed mode.